Deterministic stream example

README.md

@@ -11,6 +11,35 @@ yorke xor <(echo "secret message") <(cat /dev/urandom | tee key.txt) > cipher.tx
 yorke xor cipher.txt key.txt
 ```
 
+Encrypt a message with a deterministic, pseudo-random stream:
+
+```bash
+yorke xor <(echo "secret message") <(yorke sha256 `uuidgen | tee key.iv`) > cipher.txt
+yorke xor cipher.txt <(yorke sha256 `cat key.iv`) | xxd
+```
+
+WARNING: Never re-use the same initialization vector! It is feasible to recover
+the initialization vector by XOR'ing two ciphertexts generated against the
+common stream. Observe the following:
+
+```bash
+yorke xor <(echo "SSN: 512-73-5461") <(yorke sha256 `uuidgen | tee key.iv`) > cipher1.txt
+yorke xor <(echo "SSN: 389-16-2734") <(yorke sha256 `cat key.iv`) > cipher2.txt
+
+xxd cipher1.txt
+  0000000: 641a c768 a61c 4d2e dd58 abd9 ad05 451c  d..h..M..X....E.
+  0000010: 17                                       .
+
+xxd cipher2.txt
+  0000000: 641a c768 a61a 4425 dd5e aed9 aa06 4019  d..h..D%.^....@.
+  0000010: 17                                       .
+
+yorke xor cipher1.txt cipher2.txt | xxd
+  0000000: 0000 0000 0006 090b 0006 0500 0703 0505  ................
+  0000010: 00
+
+```
+
 # Installation
 
 ```bash